1. Field of the Invention
The present invention relates to a lubricant applying device in an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses, such as copying machines, facsimile machines, and printers, generally include a photosensitive drum and an intermediate transfer member. The photosensitive drum and the intermediate transfer member serve as image carriers. Japanese Patent Application Laid-open No. H05-323704, for example, discloses a conventional image forming apparatus including a photosensitive drum and an intermediate transfer member.
Two types of image forming apparatuses are popular in the marketplace. In the first type a photosensitive drum serves as an image carrier, and in the second type an intermediate transfer member and a photosensitive drum together serve as an image carrier.
In the first type, the photosensitive drum is normally in the form of a drum or a belt. The photosensitive drum rotates in a predetermined direction, and discharge process, exposure process, and developing process are performed with respect to the rotating photosensitive drum thereby forming a toner image onto the photosensitive drum. Transfer process is performed with respect to the toner image on the photosensitive drum thereby transferring the toner image onto a recording medium. The recording medium can be an intermediate transfer member or a paper.
On the other hand, in the second type, both the photosensitive drum and the intermediate transfer member are normally in the form of a drum or a belt. A toner image is formed in the same manner as the first type on the photosensitive drum in accordance with rotation of the intermediate transfer member in a predetermined direction. The toner image is first transferred from the photosensitive drums to the intermediate transfer member by a primary transfer process, and then the toner image is transferred from the intermediate transfer member to a recording medium by a secondary transfer process. The recording medium can be a paper.
In both the first type and the second type, once the transfer of the toner image is complete, wastes including residual toners or paper powders that remain on the photosensitive drum or the intermediate transfer member are removed by performing cleaning process with a cleaning unit.
A cleaning blade is widely used as a cleaning unit. The cleaning blade is arranged to make a physical contact with a rotating image carrier so as to scrape wastes from the surface of the image carrier. Such a cleaning blade is generally made of rubber, realizing a cheaper and simpler structure with better cleaning performance. Sometimes a brush roller that can electrostatically remove wastes is used.
A higher image quality can be achieved if the toner particles are spherical and minute. In order to satisfy the recent increasing demand for achieving higher image quality, toners with perfectly spherical and minute toner particles are being used. It is difficult, however, to remove wastes that contain such perfectly spherical and minute toner particles with the conventional cleaning blades or brush rollers.
For example, polymerized toner, such as SPR-C toner, is increasingly used in the image forming apparatus for achieving higher image quality. However, the SPR-C toner contains uniformly distributed wax material, so that the wax material is not sufficiently deposited onto the image carrier when the toner sticks to the image carrier. If the wax material that is deposited is insufficient, coefficient of friction of the surface of the image carrier increases as the time elapses. Moreover, cleaning performance decreases as the coefficient of friction increases.
Furthermore, toners with ultra-fine particles are being used for achieving higher image quality. However, ultra-fine particles are more likely to pass through even smaller gaps, slits, or holes in the cleaning blade or the brush roller. Specifically, when dimensional accuracy or assembly accuracy of the cleaning blade or the brush roller is less, or when vibration occurs on a portion of the cleaning blade or the brush roller, more toner particles pass through gaps, slits, or holes in the cleaning blade or the brush roller. Thus, cleaning performance decreases.
Because the cleaning blade is in physical contact with the image carrier, friction occurs between the two. Such friction result into abrasion of the cleaning blade and the image carrier thereby reducing the lifetimes of the cleaning blade and the image carrier. Furthermore, the cleaning blade may bend if the coefficient of friction is too high. Bending of the cleaning blade may stop certain functions of the image forming apparatus, or cause failure of the entire image forming apparatus.
For lengthening the lifetime of the image carrier and maintaining higher image quality, it is necessary to suppress damage of the image carrier, the cleaning blade, and to improve the cleaning performance. Moreover, it is necessary to prevent filming that is another cause of degradation of image quality. Filming is the phenomenon in which toners get firmly stuck onto the surface of the image carrier due to various reasons such as pressing force, and heat generated because of the friction between the cleaning blade and the image carrier.
In one of the conventional techniques, a lubricant is applied onto the image carrier for improving the cleaning performance and preventing filming.
It is necessary to stably apply an appropriate amount of the lubricant to the image carrier. If the applied lubricant is too much, coefficient of friction of the surface of the image carrier excessively decreases, decreasing amount of toners held on the image carrier. As a result, an undesirable image, such as a so-called moth eaten image, may be formed. On the other hand, if the applied lubricant is too less, coefficient of friction increases, resulting in damage to the parts.
Various techniques are known for adjusting the amount of the applied lubricant. For example, for adjusting the amount of the applied lubricant pressure between the lubricant and the brush roller can be adjusted, rotation speed of the brush roller can be adjusted, or hardness of the brush roller can be adjusted.
It is also known that amount of the lubricant applied varies depending on the state of the lubricant being in contact with the brush roller. For example, if the lubricant applied on the image carrier has corners or bumps, where the brush roller can eat into, consumption of the lubricant largely increases compared to when the brush roller slides smoothly over the surface of the lubricant. When the bumps in the lubricant become flat over time because they are scrapped off by the brush roller, the amount of applied lubricant largely decreases. There are reports that the decrease of the amount of the lubricant to be applied after using the lubricant was one tenth of that at the time of beginning of use of the lubricant.
On the other hand, if the brush roller eats in the lubricant, rotational torque of the brush roller increases. Furthermore, such a brush roller is left as it is for a long time, hairs of the brush roller may be become angled.
Thus, it is not preferable that the lubricant applied on the image carrier has corners or bumps.
When the lubricant is applied onto the image carrier by rotating the brush roller in a predetermined direction, the lubricant may be slid to a down stream side in the predetermined direction due to rotation of the brush roller, and may generate corners or bumps into which the brush roller can eat into. In consideration of above situation, Japanese Patent Application Laid-open No. 2002-268397 discloses a conventional technology for previously shifting a position of the lubricant to the upstream side in a rotation direction of the brush roller.
According to the conventional technology, such a situation where the brush roller eats into the corners or the bumps of the lubricant occurs due to defects in the mechanism for holding the lubricant. Such a mechanism generally includes a first member for holding the lubricant, a second member for guiding the lubricant on the first member to come into contact with or away from the brush roller, and a third member arranged between the first member and the second member to bias the lubricant toward the brush roller. A gap is kept between the first member and the second member. Such gap is useful if there is a need to change a position of the first member depending on a position of the second member. The gap also functions as a buffer for dimensional error. Moreover, it is easy to assemble the first member and the third member when the gap is present. Because of the gap, however, the lubricant comes into contact with the brush roller when the brush roller rotates, so that the first member inclines toward the second member. As a result, the lubricant also inclines toward the brush roller.
In other words, it is difficult to avoid eating of the brush roller into corners or bumps of the lubricant. The conventional technology, therefore, proposes to previously shift any one of the first member to the third member to the upstream side in the rotation direction of the brush roller thereby shifting a position of applying the lubricant to the upstream side.
However, the amount of such shift will vary depending on dimensional error or assembly accuracy of the first member to the third member. In other words, the amount of the shift must be adjusted depending on the situation or the brush roller may eat into the corners or the bumps even when the position of the lubricant is shifted.
Furthermore, if the shift is excessively large, the brush roller fails to come into contact with some portions of the lubricant, so that use efficiency of the lubricant decreases, resulting in loss of the lubricant. As a result, economic efficiency decreases, and lifetimes of the lubricant and the image forming apparatus is shortened. Thus, use efficiency of the lubricant may be degraded even when a position of the lubricant is shifted.